4-Amino-3-hydroxybutyric acid and its ester derivatives are synthetic intermediate important for the production of 4-hydroxy-2-pyrrolidinone. This compound is derived from 4-azido-3-hydroxybutyric acid or its ester derivatives through reduction or the other methods (Tetrahedron, 46, 4227 (1990), JP-A-Hei-8-119935, etc.).
However, the ring-closing reaction of a 4-amino-3-hydroxybutyric acid derivative to 4-hydroxy-2-pyrrolidinone requires an expensive condensation agent such as hexamethyldisilazane when 4-amino-3-hydroxybutyric acid is used as a starting material (Synthesis, 1978, P.614).
The ring-closing reaction of 4-amino-3-hydroxybutyric acid ester to 4-hydroxy-2-pyrrolidinone can be carried out by heating 4-amino-3-hydroxybutyric acid ester in a solvent such as alcohol. By only such heat treatment, the reaction takes long time since the reaction rate of the ring-closing reaction is low. Also, the isolated yield is reduced because of unreacted 4-amino-3-hydroxybutyric acid ester and the other by-products.
Further, 4-hydroxy-2-pyrrolidinone having a high optical purity cannot be obtained by recrystallization, in the case of 4-hydroxy-2-pyrrolidinone having a low optical purity derived from an optically active starting material having a low optical purity.